1. Field of the Invention
The present invention relates to a phase-shifting mask and more particularly, to a phase-shifting mask for making a semiconductor device and a method for manufacturing the same.
2. Background of the Related Art
In photolithography processes which are commonly used for manufacturing semiconductor devices, a photomask including a portion transmitting light in a desired form of a semiconductor device and a portion shielding light, has very frequently been used. That is to say, a conventional photomask includes a transparent pattern and a light-shielding pattern, thus permitting selective exposure. However, as the pattern density is increased, light diffraction limits improvement of the resolution. Therefore, much research and development has been directed to improving resolution by using a phase-shifting mask.
In a technique using a phase-shifting mask, there is utilized a combination of a transparent region and a phase-shifting transparent region. Herein, in the transparent region, light is transmitted. In the phase-shifting transparent region, the light to be transmitted is phase-shifted by about 180.degree.. This technique prevents the customary decrease in resolution between the pattern created by the light-shielding and the transparent regions. Throughout the development of manufacturing techniques for masks, various masks have been introduced by applying light phase differences that thus improve on the limitations of optical resolution.
Levenson initially started the alternate type phase-shifting mask as a phase-shifting mask, and Nitayama et al. made a phase-shifting mask of a rim type in order to improve resolution of a contact hole.
A conventional method for manufacturing a phase-shifting mask is now discussed with reference to the attached drawings.
FIGS. 1a to 1h are cross-sectional views showing a manufacturing process for a conventional phase-shifting mask.
First, shown in FIG. 1a, a light-shielding layer 2 and a first photoresist layer PR.sub.1 are sequentially formed on a transparent substrate 1. In this case, the light-shielding layer 2 is made of, for example, Cr.sub.2 O.sub.5.
Secondly, using exposure and development, the first photoresist layer PR.sub.1 is patterned to form a photoresist pattern arranged at predetermined intervals, thereby defining shielding regions, as shown in FIG. 1b.
Thereafter, as shown in FIG. 1c, with the first photoresist pattern PR.sub.1 serving as a mask, the light-shielding layer 2 is selectively removed to form a light-shielding layer pattern 2a. The exposed transparent substrate 1 thus provides opening regions 3 through which light may be transmitted.
Next, the remaining first photoresist layer PR.sub.1 on the shielding layer pattern 2a is removed, as shown in FIG. 1d.
Subsequently, on the entire surface of the transparent substrate 1 inclusive of the light-shielding pattern 2a, there are sequentially formed a spin on glass (SOG) layer 4 and a second photoresist layer PR.sub.2, as shown in FIG. 1e. In this case, as a phase-shifting layer, the SOG layer 4 is formed thick enough to cause a desired phase shift as regards the exposure beam. Due to step coverage of the opening region 3 and the light-shielding layer pattern 2a, the second photoresist layer PR.sub.2 and the SOG layer 4 are formed to have different thicknesses at the boundary A between the opening region 3 and the light-shielding layer pattern 2a. At this time, the thicknesses of the layers PR.sub.2 and 4 are thicker at the boundary A.
Referring to FIG. 1f, utilizing exposure and development, the second photoresist layer PR.sub.2 is patterned so that the second photoresist layer PR.sub.2 is left on the opening region 3 at only one side of the light-shielding layer pattern 2a. In this case, the second photoresist layer pattern PR.sub.2 overlaps with the light-shielding layer pattern 2a by a predetermined amount. That is, arrangement tolerance is utilized.
Next, utilizing the second photoresist layer pattern PR.sub.2 as a mask, the SOG layer 4 is selectively removed so that the SOG layer 4 is left on the opening region 3 at only one side of the light-shielding layer pattern 2a, as shown in FIG. 1g.
Finally, as shown in FIG. 1h, the remaining second photoresist layer PR.sub.2 is removed so that there is formed a phase-shifting mask which transmits light of the opposite phase as a result of the remaining SOG layer 4.
Such a conventional phase-shifting mask as described above has several disadvantages. For example, due to the step coverage between a light-shielding layer and an opening region, the thickness of a phase-shifting layer formed over the opening region is not uniform, resulting in a phase-shifting error of the light which has crossed the phase-shifting layer. Thus, it is difficult to transcribe a precise pattern by using a conventional phase-shifting mask, and it is not easy to reproducibly provide a phase-shifting mask of a good reliability.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.